Pen cap



FIG. 1 is an upper front right perspective view of a pen cap showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right side elevation view thereof, with the left side elevation view being a mirror image of the right side elevation view;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines shown in FIGS. 1, 4, 5, and 6 illustrate environmental subject matter and form no part of the claimed design. 

The ornamental design for a pen cap, as shown and described. 